I think it is definitely usable, although risky as a first name choice. It's unusual, so you may get a couple of double takes, and it would be very important that he is an attractive teenager and man. In that way, I think it is a lot to live up to. How will an awkward preteen deal with the expectation that he be a "fox"? My nephew's name is Cub, which is a similar style of name. We definitely thought it was strange when we first heard that they were planning to use it, but we have grown to accept it, and can't picture him with a different name. And they have gotten so many compliments on their name choice. Of your other choices, my favorites are Harrison and Crosby. I absolutely love the breezy laid back feel of Crosby!

How will an awkward preteen deal with the expectation that he be a "fox"?

This. I think it is usable, but a socially awkward teen boy may feel uncomfortable with the name fox, although fox isn't really popular slang for attractive person anymore, still, a bit awkward. I actually really like it, though. In fact, I may put it on my list for boys' middle names now that the name has been brought to my attention again. Also another vote for HarrisonFox; very nice, although it is reminiscent of HarrisonFord.